This invention relates generally to electroplating apparatus, and more specifically, relates to apparatus useful in the electroplating of metals onto lengths of metallic base stock.
In numerous applications pertaining to the fabrication of electronic components, connectors, circuit boards and the like, a requirement exists for electroplating or otherwise depositing a precious metal, such as gold or palladium, or an alloy such as palladium-nickel onto a surface of a non-precious metal such as nickel or the like, for the purpose of improving the electrical and wear characteristics of the base metal, at least at the portion thereof where electrical connections are to be effected. Thus a metal such as gold is useful for such purposes because of its excellent and uniform electrical interface properties, its relative unalterability, and its high solderability.
At one time, it was relatively common to provide precious metal gold electroplating over an entire surface of a base conductor or face of an electronic component, even though only a very limited portion of the surface being plated was actually intended to receive the electrical connections. Because, however, of various factors, including enormous increases in the cost of gold, and of other precious metals, efforts have been made in recent years to devise apparatus and methods for electroplating the precious metal only onto those portions of the base material at which the ultimate electrical connections are to be made. The savings which can result from the use of these selective electroplating techniques are relatively enormous.
In one particular method for fabricating electronic connectors, a continuous strip of a base material having a desired surface, such as of nickel, is subjected to a series of punching and forming operations, such that terminal connectors for electrical components are eventually formed toward what were originally the lateral edges of the strip. For present purposes the important point to note is that as one aspect of fabrication methods of this type, the continuous metal strip, prior to the punching and forming operations, preferably has deposited thereupon longitudinally extending stripes of a precious metal such as gold. These precious metals, e.g. gold stripes, can, for example, extend along the lateral portions of the metal strip, or one or more such stripes can extend longitudinally at positions displaced from the lateral edges. Ultimately, these stripes (or lines) will define the electrical connection areas in the devices which are fabricated from the metal base strip.
As mentioned, the surface which is selectively electroplated with the precious metal is preferably nickel, but therein lies the problem. A strip formed solely from nickel is expensive to produce and, furthermore does not have the desired physical characteristics to be handled by the apparatus used for precious metal electroplating. It, therefore, is common practice to electroplate a base metal, such as copper, or a copper alloy, with the nickel to provide the desired surface. The resultant nickel surface, however, must be uniform and of a thickness suitable for the ultimate use of the strip after the precious metal has been applied.
Also to be noted, is that while the discussion thus far has been especially directed at an ultimate product wherein a precious metal is deposited upon the nickel, there are also instances wherein the base metal strip plated with nickel alone, may comprise, per se, a suitable product for a desired application. In this event as well, the nickel plating must have the required uniformity, high wear resistance, and the like.
Experience has shown that serious problems are encountered in securing the availability of the necessary nickel-plated strip with the nickel of the desired thickness and uniformity.
In a typical production line, the base strip upon which the precious metal is to be applied, may indeed be initially plated with nickel as aforementioned, and thus the nickel-plated strip may be regarded as an "intermediate" in the overall operation proceeding from base strip to finished precious metal-plated product. Here, however, it has been found that a bottle-neck is created in the production line because of the time and/or the size of the apparatus heretofore required to produce the intermediate material. With conventional plating apparatus, increasing the current density in an effort to effect an increase in the plating rate, generally results in a degradation of the quality of the plated deposit. There is, therefore, an important need for apparatus which will make this operation faster without requiring more or larger equipment or which will permit the use of smaller equipment for equal electroplating capacity.
It is, accordingly, an object of the present invention, to provide electroplating apparatus which permits a reduction in the time required to electroplate a unit of surface.
It is another object of the invention, to provide apparatus of the character indicated, which permits the strip to be electroplated to be fed at increased rates.
It is a further object of the invention to provide apparatus of the character indicated which permits smaller equipment to provide equivalent electroplating capacity.
These and other objects and advantages of the invention will be readily apparent from the following description of illustrative embodiments, taken in connection with the accompanying drawings.